Embodiments of the present invention relate to deflection of a shaped particle beam while writing a circuit design pattern on a substrate.
Pattern generators are used to write patterns on substrates, such as masks for semiconductor fabrication, semiconductor wafers, displays and circuit boards, magnetic bubble fabrication, and optical data storage media fabrication. Patterned lithographic masks are used to transfer a circuit design pattern into a substrate, such as a semiconductor wafer or dielectric to fabricate integrated circuits, printed circuits (PCB), displays, and other patterned boards. A typical process for fabricating a lithographic mask includes, for example, (i) forming a layer of a metal-containing material on a radiation permeable plate, (ii) forming a resist layer on the metal-containing layer to create a blank lithographic mask, the resist layer being sensitive to a particle beam such as an electron or ion beam, (iii) writing a pattern on the mask by selectively exposing the blank lithographic mask to the modulated particle beam, (iv) developing the exposed material to reveal a pattern of features, (v) etching the revealed portions of the metal-containing material between the resist features to transfer the pattern captured in the resist features into the metal-containing material, and (vi) stripping residual resist from the lithographic mask.
The pattern is written by selectively exposing an energy sensitive resist layer on the substrate to a modulated particle beam. The particle beam, which can be an electron or ion beam, is formed in a beam column having discrete components that focus, blank and deflect the electrons or ions to write a pattern on a substrate. Conventional electron beam columns provide an electron beam which is flashed while a substrate is moved, as for example described in U.S. Pat. No. 6,262,429 to Rishton et al.; U.S. Pat. No. 5,876,902 to Veneklasen et al.; U.S. Pat. No. 3,900,737 to Collier et al.; and U.S. Pat. No. 4,243,866 to Pfeiffer et al.; all of which are incorporated herein by reference in their entireties. The electron beam column has electrostatic deflectors and beam shaping aperture plates. The deflectors deflect the electron beam across the aperture plates to control the shape of an electron beam flash in the writing process.
Conventional deflectors often do not provide sufficiently high beam deflecting accuracies to write circuit design patterns having features with dimensions on the order of less than 50 nm—this feature size is more than 2½ times smaller than conventional feature sizes of over 130 nm. A highly accurate deflector is also needed to provide accurate beam deflection when writing patterns in multiple successive layers that need to be overlaid upon one another with good accuracy. A schematic diagram of a conventional deflector 10 having a single voltage drive 12 that provides complementary voltages to two parallel facing deflector plates 14, 16 shown in FIG. 1. The voltage drive 12 comprises a digital to analog converter (DAC) 18 which converts an input digital code to an analog voltage, which is then passed to an amplifier 20 which amplifies the analog voltage and passes complementary positive and negative voltages to the deflector plates 14, 16. The voltage between the deflector plates deflects the particle beam 22 by an amount proportional to magnitude of the voltage. However, such conventional deflectors have limited beam deflection accuracy. For example, the DAC of the deflector often provides a non-linear voltage response to an input digital signal which contributes to deflection inaccuracy. Typically, the nonlinear response occurs at the segment boundaries of the digital code. Custom integrated circuit DACs can also be used to avoid such non-linearities, however, such DACs are quite expensive and often have slow processing speeds
Thus, it is desirable to have a deflector capable of accurately controlling particle beam deflection to provide high resolution patterning. It is desirable to have a deflector that can write a pattern onto a substrate with adequate resolution without sacrificing process throughput.